X ( 2 , 17 , 3 , 18 ) X ( 4 , 16 , 5 , 15 ) X ( 6 , 2 , 7 , 1 ) X ( 8 , 3 , 9 , 4 ) X ( 10 , 6 , 11 , 5 ) X ( 11 , 21 , 12 , 20 ) X ( 13 , 1 , 14 , 22 ) X ( 16 , 9 , 17 , 10 ) X ( 18 , 8 , 19 , 7 ) X ( 19 , 15 , 20 , 14 ) X ( 21 , 13 , 22 , 12 ) {\displaystyle X(2,17,3,18)X(4,16,5,15)X(6,2,7,1)X(8,3,9,4)X(10,6,11,5)X(11,21,12,20)X(13,1,14,22)X(16,9,17,10)X(18,8,19,7)X(19,15,20,14)X(21,13,22,12)}